Ruby - Socket Programming

Ruby provides two levels of access to network services. At a low level, you can access the basic socket support in the underlying operating system, which allows you to implement clients and servers for both connection-oriented and connectionless protocols.

Ruby also has libraries that provide higher-level access to specific application-level network protocols, such as FTP, HTTP, and so on.

This chapter gives you an understanding on most famous concept in Networking − Socket Programming.

What are Sockets?

Sockets are the endpoints of a bidirectional communications channel. Sockets may communicate within a process, between processes on the same machine, or between processes on different continents.

Sockets may be implemented over a number of different channel types: Unix domain sockets, TCP, UDP, and so on. The socket provides specific classes for handling the common transports as well as a generic interface for handling the rest.

Sockets have their own vocabulary −

A Simple Client

Here we will write a very simple client program, which will open a connection to a given port and given host. Ruby class TCPSocket provides open function to open such a socket.

The TCPSocket.open(hosname, port ) opens a TCP connection to hostname on the port.

Once you have a socket open, you can read from it like any IO object. When done, remember to close it, as you would close a file.

The following code is a very simple client that connects to a given host and port, reads any available data from the socket, and then exits −

require 'socket'        # Sockets are in standard library

hostname = 'localhost'
port = 2000

s = TCPSocket.open(hostname, port)

while line = s.gets     # Read lines from the socket
   puts line.chop       # And print with platform line terminator
end
s.close                 # Close the socket when done

A Simple Server

To write Internet servers, we use the TCPServer class. A TCPServer object is a factory for TCPSocket objects.

Now call TCPServer.open(hostname, port function to specify a port for your service and create a TCPServer object.

Next, call the accept method of the returned TCPServer object. This method waits until a client connects to the port you specified, and then returns a TCPSocket object that represents the connection to that client.

require 'socket'                 # Get sockets from stdlib

server = TCPServer.open(2000)    # Socket to listen on port 2000
loop {                           # Servers run forever
   client = server.accept        # Wait for a client to connect
   client.puts(Time.now.ctime)   # Send the time to the client
   client.puts "Closing the connection. Bye!"
   client.close                  # Disconnect from the client
}

Now, run this server in background and then run the above client to see the result.

Multi-Client TCP Servers

Most servers on the Internet are designed to deal with large numbers of clients at any one time.

Ruby's Thread class makes it easy to create a multithreaded server.one that accepts requests and immediately creates a new thread of execution to process the connection while allowing the main program to await more connections −

require 'socket'                 # Get sockets from stdlib

server = TCPServer.open(2000)    # Socket to listen on port 2000
loop {                           # Servers run forever
   Thread.start(server.accept) do |client|
   client.puts(Time.now.ctime)   # Send the time to the client
   client.puts "Closing the connection. Bye!"
   client.close                  # Disconnect from the client
   end
}

In this example, you have a permanent loop, and when server.accept responds, a new thread is created and started immediately to handle the connection that has just been accepted, using the connection object passed into the thread. However, the main program immediately loops back and awaits new connections.

Using Ruby threads in this way means the code is portable and will run in the same way on Linux, OS X, and Windows.

A Tiny Web Browser

We can use the socket library to implement any Internet protocol. Here, for example, is a code to fetch the content of a web page −

require 'socket'
 
host = 'www.howcodex.com'     # The web server
port = 80                           # Default HTTP port
path = "/index.htm"                 # The file we want 

# This is the HTTP request we send to fetch a file
request = "GET #{path} HTTP/1.0\r\n\r\n"

socket = TCPSocket.open(host,port)  # Connect to server
socket.print(request)               # Send request
response = socket.read              # Read complete response
# Split response at first blank line into headers and body
headers,body = response.split("\r\n\r\n", 2) 
print body                          # And display it

To implement the similar web client, you can use a pre-built library like Net::HTTP for working with HTTP. Here is the code that does the equivalent of the previous code −

require 'net/http'                  # The library we need
host = 'www.howcodex.com'     # The web server
path = '/index.htm'                 # The file we want 

http = Net::HTTP.new(host)          # Create a connection
headers, body = http.get(path)      # Request the file
if headers.code == "200"            # Check the status code   
   print body                        
else                                
   puts "#{headers.code} #{headers.message}" 
end

Please check similar libraries to work with FTP, SMTP, POP, and IMAP protocols.

Further Readings

We have given you a quick start on Socket Programming. It is a big subject, so it is recommended that you go through Ruby Socket Library and Class Methods to find more details.